I do know this sounds bad, but a lot of the "elder" cachers in the group have bad feelings about the marina district. A member of the group attempted to place a cache there and there was A LOT of problems with the security that patrols that park.
As for the Zoo issue, the only event planned for May 15th is the Dart Frog Dash, a 5k run for the zoo, with a 1k kids walk/run. So my opinion is that parking should not be an issue. Especially with the park right there and the neighborhood surrounding the area.
I along with another cacher will volunteer to get this completely organized along with an event page, ect... Any objections, please speak now, we plan on getting a move on planning next week sometime if there are no objections.